Fable 3 on windows - Coop is a shame / feeling scammed

Hello, I bought the game Fable 3 on PC this week, bought without checking online which is a bit stupid, anyway... Bought it to play it with my wife in coop, as the box says we can play in COOP. As the game can also be played online, i thought it would be COOP in LAN. The box didn't say split screen! And then we install the game, and the coop is only split screen! Who the **** plays with 2 keyboards and 2 mouses on the same computer? And to play in LAN, we need in fact to connect ONLINE with 2 KEYS, buying the game twice. I'm feeling so scammed.. I read that the XBOX version was allowing lan play. As i don't want to pay another key (50$), I'd like to get my money back (50$), the store where i bought it doesn't take it back. How should i do? Thanks, Kevin